implement my own std::myless

I am trying to understad how std::less is implemented so I can say

template <typename T>
struct myless
{
    constexpr bool operator()(const T &lhs, const T &rhs) const
    {
        return lhs < rhs;
    }
};

template <typename A, typename B, typename U = std::myless> // std::less works
bool f(A a, B b, U u = U())
{
    return u(a, b);
}

int main() 
{
    std::cout << std::boolalpha;

    std::cout << f("AB/CD", "CD/AB",) << '\n';
    std::cout << f(100, 10) << '\n';
}

This doesn't work. Any suggestions?